Studies in this laboratory have shown qualitative and quantitative alterations in several different immunofunctional cell types following topical application of phorbol diesters at tumor- promoting doses. Evidence for a role of such alterations in the promotion process was thereby provided, and indicated in which stageof the latter individual changes were most important. We havedemonstrated in this way that overall promoter-induced spleen cell proliferation was predominantly a consequence of inflammation, and may be relevant only in the later stages of promotion. On the other hand promoter-induced proliferation of GMCFU progenitor cells was apparently not, and was inhibited by inhibitors of promotion with inhibitory activity toward specific pathways of arachidonic acid metabolism. These findings strongly indicated a role for GM-CFU cells in promotion, but also a need todetermine underlying mechanisms. These include whether the increase proliferation was due to i) systemic promoter effects of viarelease of soluble Interleukin 3 or Colony-Stimulating Factor fromskin cells and ii) due to increased traffic from the marrow rather than proliferation in situ. Afurther finding in this laboratory was a reduction in number of Thy1+epidermal cells following topical promoter application, together with a morphological change in these and Ia+ Langerhans cellsTo further investigate the responses of these cells to promoting agents, the following parameters will be measured: i) Cell densities in epidermal sheets. ii) Cellfunctions following purification by sorting: Interleukin 1production and ability to induce contact hypersensitivity CH) for Langerhans cells, and ability to down-regulate CH forThy-1+ cells. The role of observed alterations in the above parameters in the tumor promotion process will be assessed using: i) Agents with different relative tumor-promoting and inflammatory activities. ii) Agents which inhibit promotion and inflammation to different degrees. iii) Brief and prolonged exposures to the above agents and modifiers, comparing resultant inflammatory and immunomodulatory responses. Inflammatory/promoting agents will be used with inflammatory activity which persists to different degrees. Additional studies in initiated animals will also enable alterations in immune cells to be temporally related to tumor appearance.